Abstract
Prenatal diagnosis of trisomy 21 requires an invasive test in women considered to be at high risk after screening. At present there are four screening tests. For a 5% false positive rate, the sensitivities are approximately 30% for maternal age alone, 60-70% for maternal age and second-trimester maternal serum biochemical testing, 75% for maternal age and first-trimester fetal nuchal translucency (NT) scanning, and 90% for maternal age with fetal NT and maternal serum free [beta]-human chorionic gonadotropin ([beta]-hCG) and pregnancy-associated plasma protein-A (PAPP-A) at 11-14 weeks. This article examines the methodology of first trimester screening and summarises the results from the implementation of this method. The early pregnancy scan was initially introduced with the primary intention of measuring the fetal crown-rump length to achieve accurate pregnancy dating. During the last decade, however, improvement in the resolution of ultrasound machines has made it possible to describe the normal anatomy of the fetus and diagnose or suspect the presence of a wide range of fetal defects in the first trimester of pregnancy. An important component of the 11-14-week scan is measurement of fetal nuchal translucency thickness (NT; Figure 1) which provides effective screening for chromosomal abnormalities, major defects of the heart and great arteries, and a wide range of skeletal dysplasias and genetic syndromes. As with the introduction of any new technology into routine clinical practice, it is essential that those undertaking the 11-14-week scan are adequately trained and their results are subjected to rigorous audit. This article reviews the application of NT measurement in routine obstetric care
| Original language | English |
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| Pages (from-to) | 167 - 176 |
| Number of pages | 10 |
| Journal | Perinatology |
| Volume | 5 |
| Issue number | 4 |
| Publication status | Published - Jul 2003 |